Effect of Excitonic Coupling and Disorder on Nonradiative Decay of Molecular Aggregates: A TD-DMRG Study

Coherent exciton delocalization significantly impacts nonradiative decay processes in molecular aggregates, as evidenced by recent experimental and theoretical studies. Since delocalization is influenced by excitonic coupling strength, aggregate size, and both dynamic and static disorder, in this study, we employ the numerically exact time-dependent density matrix renormalization group algorithm combined with ab initio quantum chemistry calculations to investigate these effects on the nonradiative decay rate (k_nr) in J-aggregates of dihexylquaterrylene. Our findings reveal that k_nr initially decreases and then increases with excitonic coupling strength, consistent with our previous study for a two-mode model. In the weak coupling regime, k_nr decreases slightly with aggregate size, whereas in the strong coupling regime, it rises rapidly. Dynamic disorder generally enhances k_nr, except in the phonon-assisted regime, where it promotes exciton delocalization and reduces effective electron-vibration coupling. Static disorder consistently increases k_nr by reducing the energy gap and localizing the exciton. These results provide valuable insights into optimizing excitonic coupling and minimizing disorder to enhance the photoluminescence quantum efficiency of molecular aggregates.